Climate and Atmospheric Circulation Change During the Last Millennium Revealed from Paired δ13C and δ18O Record from Sphagnum Moss Cellulose of a Mountaintop Peatland in Northeast China

There is a general good understanding of hydroclimate change in Northeast China near the northern limit of the East Asian summer monsoon influence. However, we know much less about change in temperature and atmospheric circulation. Recently developed dual δ¹³C and δ¹⁸O approach from peat core archive provides not only a proxy for moisture/wetness change but also constraint for interpreting precipitation isotope. Northeast China receives most moisture from the Eurasian Continent predominantly through the westerlies and some moisture through warm air masses from the North Pacific. Changes in the proportion of these moisture sources would affect both summer precipitation and temperature that affect Sphagnum growth and its isotopic signature. Here we combined macrofossil data and coupled C and O isotope analysis of Sphagnums moss cellulose from a well-dated peat core retrieved from a Sphagnum-dominated ombrotrophic (rain-fed) bog to reconstruct regional climate and moisture sources over the last millennium. Our results show a decrease of ~6‰ in δ¹³C from -23 to -29‰, with large-magnitude fluctuations, over the last 1000 years, suggesting a long-term drying trend. The lack of a negative correlation between δ¹³C and δ¹⁸O suggests that peatland wetness and evaporative enrichment are not—but δ¹⁸O in precipitation is—the dominant factor affecting cellulose δ¹⁸O. An abrupt decrease at 1400 AD of 4‰ in δ¹⁸O from >21‰ to ~17‰ represents the transition from the warm/wet Medieval Warm Period (MCA) to the cold/drying Little Ice Age (LIA), reaching the lowest δ¹⁸O value of ~15‰ at 1800 AD. The increase in δ¹⁸O to 19‰ after 1900 AD shows a post-LIA warming. Enhanced moisture transport from the North Pacific—perhaps associated with enhanced summer monsoon—might have contributed to the warm/wet MCA. Three short intervals with pronounced low δ¹³C and δ¹⁸O values occurred at 1400-1350 AD, the 19^th Century, and the 1990s, suggesting extreme cold and dry periods with reduced Pacific moisture inputs. The driest period with consistently low δ¹³C value of <-25‰ occurred after 1990 AD, with corresponding increase in dry-adapted moss Polytrichum. We argue that there were major shifts in atmospheric circulation and associated hydroclimate and temperature change during the MCA, LIA and Recent Warming Period in Northeast China.